Implantable medical devices (IMDs) and external, e.g., wearable, medical devices, including implantable pacemakers and implantable cardioverter-defibrillators (ICDs), record cardiac electrogram (EGM) signals for sensing cardiac events, e.g., P-waves and R-waves. IMDs detect episodes of bradycardia, tachycardia and/or fibrillation from the sensed cardiac events and, in some cases, respond to the episodes as needed with pacing therapy or high-voltage anti-tachyarrhythmia shocks, e.g., cardioversion or defibrillation shocks. Some IMDs include, or are or part of a system that includes, sensors that generate other physiological signals, such as signals that vary based on patient movement or activity, cardiovascular pressure, blood oxygen saturation, edema, or thoracic impedance. Physiological parameters determined based on such signals may be used to assist in the detection of arrhythmia, as well as the detection or monitoring of other cardiac conditions, such as heart failure or infarction, or, more generally, cardiac health.